This invention relates to an apparatus for setting a workpiece correctly on a sewing machine designed to sew a zipper to a skirt.
Referring to FIG. 11A, a zipper S is generally sewed to a skirt C with the zipper positioned between the waist line and the hip line. As this portion of the skirt must be curved to conform to the body, the segment of material to which the zipper must be sewn is curved along a bias as shown in FIG. 11B.
To sew a zipper to a section with such a bias curve, a specially designed sewing machine M, shown in FIG. 13, and a cassette 1, shown in FIG. 12, were previously used. Accordingly, referring to FIG. 12, cassette 1 would be placed on a set table 2 such that lower frame 1a fit on a zipper guide 2a. Zipper F would then be placed on the zipper guide 2a so that the zipper became aligned with groove 2a.sub.1 on the zipper guide.
Skirt material C, to which the zipper was to be sewn, would then be placed on the lower frame 1a. Sides Ca.sub.1 and Cb.sub.1 of the skirt material were then aligned with the center portion of zipper F so that they met on the center line of the zipper. An upper frame 1b was then closed, engaging a spring 1c with a stopper notch 1d.sub.1 provided at fixing-bracket 1d so that the upper frame 1b clamped the zipper.
Referring now to FIG. 13, cassette 1 would then be separated from set table 2 and placed between a pressing plate Ml and a feed plate M2. An air cylinder M3, activated by a foot switch (not shown) would pull plunger M4, causing lever M5 to turn shaft M6 counter-clockwise so that lever M7, whose end is fixed to the shaft M6, turns counter-clockwise and depresses cassette 1. The foot switch (not shown) would then activate the sewing machine. A control apparatus (not shown) would control the vertical action of the needle and the X-Y motion of feed plate 2 in accordance with a predetermined stitch pattern. In this manner, a stitch line S would be performed, sewing the zipper to the skirt material, FIG. 11A.
Assuming that the zipper F and the to-be-sewn sections of material are correctly aligned in cassette 1 before sewing begins, an operator can sew the zipper to the material correctly and speedily.
More recently, an automatic setting apparatus 3 for aligning and setting a zipper on material has been introduced as shown in FIG. 14. The apparatus in FIG. 14 was described in U.S. Pat. No. 4,648,335, "Apparatus for Setting a Workpiece Correctly on a Sewing Machine" by some of the same inventors as in the present invention. According to this patent, skirt edges Ca and Cb, which are turned down, are inserted by setting plates 31a and 31b, respectively, which are positioned in V-formation. After insertion, the setting plates 31a and 31b close so that sides Ca.sub.1 and Cb.sub.1 of the to-be-sewn edges Ca and Cb meet along the inside straight lining of setting plates 31a and 31b. After edges Ca and Cb meet, upper frame 1b closes and is fixed by spring 1c, depressing the workpiece. Setting plates 31a and 31b then expand outwardly and are separated from the material C. In this manner, the zipper is correctly set on skirt material C.
V-formed setting plates 31a and 31b are closed by V-formed levers 36a and 36b. Levers 36a and 36b are activated by air cylinders 32a and 32b which are connected to the levers by drawing plungers 33a and 33b, links 34a and 34b, and pins 35a and 35b. To separate the setting plates 31a and 31b from the skirt material C, plungers 38a and 38b of air cylinders 37a and 37b (not shown) are withdrawn. This causes arm 40a to rotate counter-clockwise, keeping shaft 39a at the center of rotation, and arm 40b to rotate clockwise, keeping shaft 39b as its center. In this manner, setting plates 31a and 31b expand outwardly and are separated from the skirt.
Accordingly, with the conventional setting apparatus, when the bias curved edges Ca.sub.1 and Cb.sub.1 of to-be-sewn material sections Ca and Cb met at the straight end of setting plates 31a and 31b, the skirt material naturally shrank and became wrinkled as shown in FIG. 11C. Correct setting was thus impossble using this apparatus.